/Engine/Source/Runtime/Foliage/Public/FoliageStatistics.h
Gets the number of instances overlapping a provided box
static int32 FoliageOverlappingBoxCount ( [UObject](API\Runtime\CoreUObject\UObject\UObject) * WorldContextObject, const [UStaticMesh](API\Runtime\Engine\Engine\UStaticMesh) * StaticMesh, FBox Box )